An estimated 7 million people died due to air pollution globally in 2012, with more than half of the deaths linked to indoor smoke from cook stoves, according to a report by the World Health Organization.

Air pollution is now the "single largest environmental health risk," the U.N. health agency stated in the report. The majority of the deaths associated with air pollution were heart disease, stroke, chronic obstructive pulmonary disease and lung cancer.

"Few risks have greater impact on global health today than air pollution: the evidence signals the need for concerted action to clean up the air we all breathe," said Dr. Maria Neira, director of WHO's Department for Public Health, Environmental and Social Determinants of Health in the report.

The Western Pacific (which includes east Asia and the Pacific islands)and the Southeast Asian regions were estimated to be the hardest-hit, according to the report, with 2.8 million and 2.3 million deaths as a result of polluted air in 2012.

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In the Southeast Asian region, the bulk of it, with 1.7 million premature deaths, was attributed to indoor air pollution.

Around 3 billion people in the world rely on coal, wood and open-air fires for household cooking, according to the WHO's estimates. In India, 63% of the population uses such solid fuels for cooking. These fuels produce harmful pollutants such as fine particulate matter and carbon monoxide.

Country-specific data was not yet available in the report.

The WHO findings further noted that women in developing countries are more exposed to household air pollution than men.

"Poor women and children pay a hefty price from indoor air pollution since they spend more time at home breathing in smoke and soot from leaky coal and wood cook stoves," said Dr. Flavia Bustreo, WHO assistant director of General Family, Women and Child's Health in the report.

Meanwhile, outdoor air pollution killed an estimated 3.7 million people, with more than 80% of the deaths occurring in low- and middle-income countries.

The sources for ambient pollution include diesel engines and industrial emissions. Sixty percent of these deaths were due to cardiovascular diseases like stroke and heart disease.